list hides when selecting 2nd item

i have a dropdownbox as a list using size='15

the selected item opens a list in a gridview showing data about this item

now the strange thing occures.

the list is visible on the left, the details on the right. when i select the 2nd item in the list it disappears. this only happens on the second item (i have like 30 items)

is there some way i can make this not happen or some other type of list i should use?

all i need is a list (listboxstyle) showing my items but with the first value selected on load. using ASPX  VB.

i really have no clue why this happens
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